The present invention s related to colored and white LED lamps. A purpose of the present invention is to provide a single-chip LED lamp that is up to 250 times ore more powerful than a conventional single-chip LED lamp. Another purpose of the invention is to provide a two-chip white LED lamp that is up to 250 times more powerful than a conventional single-chip white LED lamp.
Existing single-chip LED lamps are generally of low input power, typically 40-150 milliwatts.
Designers of lamps for outdoor use have had the choice mainly of incandescent tungsten light sources, gas discharge light sources, and LED light sources. Designers of LED-based lamps requiring high power have had to resort to using clusters of single chip LED lamps, each of about 0.1 watt rating, wired in series or in parallel and housed together as a single lamp unit to achieve enhanced power. Providing a lamp unit by clustering single-chip LED lamps is very costly, since it involves making several single-chip lamps, housing them in a unit, wiring them up, and testing the final unit. U.S. Pat. Nos. 5,382,811 and 5,632,551 provide examples of cluster lamps.
Applications for high power LED colored lamps include outdoor displays, which usually have to operate in direct sunlight and so require powerful lamps, and vehicle lights and traffic lights. At present long-life LED traffic lights for use at street intersections need more than a hundred conventional single-chip LED lamps for each lamp unit. The need to use many LED lamps to provide a single LED traffic light is a disadvantage, particularly since only one tungsten light source is needed for a conventional traffic light.
Current blue-green LED traffic lights rely on gallium nitride (GaN) LED technology; whereas amber and red traffic lights rely on aluminum gallium indium phosphide (AlGaInP) technology. It is an object of this invention to provide high power single chip LED lamps in both of these technologies.
Applications for high power LED white lamps include vehicle headlights and reverse lights, vehicle internal lights, torches and other battery powered lighting devices. White single chip LED lamps are available, but they are typically of only about 0.1 watt, unless they are cluster lamps. Furthermore, they rely on a GaN chip that generates ultraviolet or blue light. All or most of this generated light energy has to be converted, using fluorescent material, into longer wavelength components to produce the white light. The light conversion results in loss of light energy. FIG. 31 illustrates the typical spectral distribution of the white light produced. This is quite different from the spectral distribution of daylight, which is represented by dotted line 437.
Prior art single-chip LED lamps having clear convergent lenses, used widely in outdoor displays, suffer not only from the fact that they are of low power but also from the fact that they project light that is not uniform. The non-uniformity is partly due to the bonding pad or pads on the chip top face, which are projected by the lamp as dark areas. The typical width of the bonding pad is about 30-40% of the width of the chip and this is large enough to interfere with achieving good uniformity of projected light even if the LED lens is defocussed relative to top face of the chip. For good quality image displays it is desirable to match the apparent brightnesses of the viewed lamps to within 5%. To achieve this it is important to reduce the non-uniformity caused by the bonding pads.
An object of the present invention is to provide a single-chip LED lamp that avoids or reduces the need for clustering.
A further object of the present invention is to provide a single chip LED lamp arranged so that light emitting portions of the chip are adjusted to be equalised in intensity.
A further object of the present invention is to provide a single chip LED lamp in which the sizes of the bonding pads relative to the size of the chip are reduced, so as to improve uniformity of light projected by a lensed lamp.
A further object of the present invention is to provide a single chip LED lamp, with input power in the region of 5-25 watts, that has low rise of the junction temperature when energised, thus prolonging the life of the lamp and reducing or eliminating the need for forced ventilation of the lamp.
A further object of the present invention is to provide a single chip LED lamp arranged so that light emitting portions of the chip that are faulty, by drawing more than their fair share of current, are starved of electrical power.
A further object of the present invention is to provide a single chip AlGaInP lamp of high power, avoiding the need for clustering lamps for an amber or red street traffic light.
A further object of the present invention is to provide an AlGaInP LED chip for an LED lamp that does not require a thick (and therefore costly) window layer, either above or below the active region, for efficient light extraction.
A further object of the present invention is to provide a white light lamp based on just two LEDs one of which has an AlGaInP active region.
A further object of the present invention is to provide a white light lamp having a spectral distribution close to that of daylight.
A further object of the present invention is to provide a high power RGB lamp that is based on two chips one of which has an AlGaInP active region.
According to an aspect of the invention an LED lamp includes an LED chip having a top face and comprising a substrate and semiconductor layers between the top face and the substrate, the semiconductor layers forming the core of a light guide extending parallel to the plane of the top face. The chip includes at least one cavity with light-emitting side walls that extends into at least one of the semiconductor layers. The chip converts guided light in the core into top light. According to another aspect of the invention guided light in the core is extracted with the aid of reflectors that are parallel to the semiconductor layers. According to yet another aspect of the invention metal tracks connected to the n-type semiconductor layer are provided that enhance the efficiency of the lamp.
According to another aspect of the invention an LED lamp includes a chip comprising at least two light emitters each having a triangular top face, the two emitters being separated by a trench.
According to another aspect of the invention a single chip LED lamp which can have input power of 5-25 watts includes an LED chip having a top face and comprising a substrate and semiconductor layers between the top face and the substrate, the semiconductor layers forming the core of a light guide extending parallel to the plane of the top face. The chip includes at least one trench, and a heat sink is attached to the top face of the chip that draws heat from the active region of the chip.
According to another aspect of the invention an LED lamp has an LED chip with a plurality of individually powered light emitting elements each provided with a fuse. This improves the yield of usable LED chips during manufacture.
According to another aspect of the invention there is provided an LED lamp comprising: an LED semiconductor core having a thickness and comprising a plurality of vertically stacked semiconductor layers; cavities in the core having side walls that divert light from the core; first and second reflectors that are below and above the core, respectively; each of the reflectors being reflective to light from the core that has an angle of incidence to the reflector of 60 degrees, the reflectors guiding light generated in the core towards the cavities; and the core being lattice-matched to GaAs and generating visible light.
According to another aspect of the invention a high power AlGaInP LED for a lamp is manufactured using the steps of: providing a member having a planar surface; providing a GaAs substrate on which an AlGaInP LED is epitaxially grown; providing an electrical terminal on the LED; joining the member to the LED; removing the GaAs substrate; and the method also including the step of providing an opening in the member positioned to be opposite said terminal. The steps are preferably carried out during wafer processing.
According to another aspect of the invention a high power AlGaInP LED for a lamp is manufactured using the steps of: providing an LED that is supported on and epitaxial with a GaAs substrate; providing a non-semiconductor substrate having lower and upper surfaces; joining the LED to the upper substrate surface using a medium having a melting temperature exceeding 300xc2x0 C.; removing the GaAs substrate; providing an ohmic contact to the LED using a process that heats the LED to more than 300xc2x0 C. and providing a surface between the LED and the lower substrate surface that is reflective to LED light incident to the surface at 60xc2x0. The steps are preferably carried out during wafer processing.
According to another aspect of the invention there is provided an LED white lamp comprising a vertical stack of just two LEDs one of which is of AlGaInP and the other of GaN (or InGaN). The AlGaInP LED generates light at very low cost per lumen compared with GaN. Thus the combination provides white light at a lower cost per lumen than a white lamp based entirely on GaN. Furthermore, the use of fluorescent material, which causes energy loss, can be avoided.
According to another aspect of the invention there is provided an LED white lamp comprising an LED in which the active region crystal lattice structure is based on several chemical elements and the ratio of one of the elements to another of them is altered during the crystal growth so as to broaden the spectral distribution of the light of the LED.
According to another aspect of the invention there is provided a high power variable color RGB lamp comprising a vertical LED stack of just two LED chips, one of which is of AlGaInP.
According to another aspect of the invention there is provided a lamp capable of generating white light, the lamp comprising a GaN chip having interleaved light emitting elements of differing colors.